Why do some cyclists expend time and energy worrying, ranting, or wondering about riders who don't wear a helmet? Why do so many experienced riders think it the height of foolishness to ride without a helmet? These are puzzling questions. Obviously helmets can help sometimes to prevent serious injuries, but not nearly so often as their indignant promoters like to believe. They simply are not that big of a deal.
Judging from accident statistics, helmet use on a bicycle can be expected to have a preventative effect roughly comparable to helmet use while driving, or helmet wearing while walking near traffic, or helmet wearing while playing on playground equipment. That is, they can have some effect, but it's hard to understand why anyone is so fanatical about it.
To think of another example, more brain injuries, more deaths, and more spent hospital dollars result each year from swimming accidents than from cycling accidents. But why isn't there a widespread movement to require life jackets while using a pool? Why not require water wings for everyone? Why do we not have people posting pithy slogans like, "no life jacket, no brain"?
Why, for that matter, doesn't anyone here post indignantly about drivers without helmets, or joggers without helmets, or ladder users without helmets?
The answer, depressingly enough, is simply that no one has yet seen a slick poster saying "courage for your arms" with a picture of some athlete swimming with water wings. No one has yet been beseiged with propaganda concerning "unhelmeted drivers". No one has yet heard their friends repeat slogans they heard in a swim shop, or an auto repair shop, that they themselves can confidently repeat and post on news groups. That's all.
It's true that some people think of some anecdote involving them or their friends that "proves" how important it is to ride with a helmet. But you don't have to know much about cycling to understand the worries concerning anecdotal evidence, such as selection bias, small samples, etc., etc. To give an example of one problem, if a pedestrian is hit by a car, knocked into the air, but walks away without injury, no one thinks how "lucky" the person was to have survived without a helmet. No one thinks about helmets at all in that case. If pedestrians _did_ wear helmets, a scene like that would become yet another occasion for a story of how a helmet saved a life. Similar problems exist for reports about cycling accidents and helmets.
But few cyclists think about this. Why? Why do cyclists, people who insist on making detailed and critical arguments about traffic planning, oil use, or just cycling in traffic, swallow all of the slogans whole about helmets?
War a helmet if you like. It might help you one day--- though I hope you never have occasion to find out. Just save the lectures for a behavior that actually warrants it.